1. Field of The Invention
One important condition for transformers/reactors to be provided with superconducting windings while at the same time becoming a commercial and competitive product in relation to transformers/reactors with conventional windings is that the unavoidable a.c. losses are minimized. In the same way as sheet-wound windings are used in conventional transformers/reactors, the superconductor can be designed as a sheet or a tape to reduce the losses. At the same time, it is very important that the orientation of the conductor relative to the direction of the magnetic field be chosen in an optimal manner. The present invention relates to a winding support body with the aid of which the conductor is oriented such that the direction of the magnetic field coincides with the plane of the conductor.
2. Description Of The Prior Art
Characteristic of superconductors is that the current density is much higher than in metallic conductors. A superconductor which is to be used in a transformer winding/reactor winding is suitably given the shape of a tape, that is, the width thereof is considerably larger than the thickness. The tape preferably consists of a number of superconducting filaments embedded into a metallic matrix. This, however, means that with such a conductor the mechanical strength of the winding is not sufficient to support the magnetic forces which may arise. Therefore, the conductor needs a mechanical support in the form of a winding support body. Since the prior art at present does not comprise transformers/reactors with superconductors, there is also no prior art regarding the design of winding support bodies for such windings.
With respect to transformers, the magnetic field configuration for two concentric windings 1 and 2 around a limb 3 of a transformer core will have an appearance as shown in FIG. 1. The substantially axial leakage flux 4 extending between the windings is deflected in a more or less radial direction at the ends of the windings in order to enter the core. This causes the ends of the windings to be traversed by a magnetic flux with a radial component which generates eddy currents in the conductor and causes losses.
It is therefore natural, in describing the prior art, to start from the technique which has been used for a long time in conventional sheet-wound transformer windings to achieve the desired orientation in relation to the direction of the magnetic field. A typical example of this technique is disclosed in U.S. Pat. No. 4,323,870. Instead of attempting to influence the field configuration, the conductor material is allowed to follow the field. This is done in such a way that the tape is formed such that the magnetic field vector at each point is tangent to the conductor surface. In this way, the current displacement can be eliminated. The accompanying FIG. 2, which is identical with FIG. 1 in the above US patent shows how sheet-wound windings can be designed to achieve this desired effect. The inward rounding towards the core limb is brought about by rounding off the winding support body 5, which is really not necessary from a mechanical point of view, at the ends towards the core limb, and the outward rounding can be performed with the aid of wedges or linings of different kinds. This method, however, entails an increased space requirement, increased radius of the windings resulting in increased losses, and a relatively time-consuming and difficult winding work.